Maturation of tomato fruit

Maturation of tomato fruit (brozova, iStockphoto)

The Life Cycle of a Tomato Plant

Let's Talk Science
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Summary

Learn about the pollination, fertilization, germination and growth of tomato plants.

Reproduction

Tomatoes belong to a group of plants known as flowering plants, also called angiosperms. The tomato plant reproduces sexually. This means that it needs both female and male organs to produce seeds. 

Every tomato seed has a tiny tomato plant inside. When the conditions are just right, tomato seeds will germinate. When the seed germinates, the radicle, or young root breaks out of the seed and grows down into the ground. Cotyledons, or seed leaves then grow up out of the ground towards the sun. Soon the plant develops its first true leaves, then more leaves and flower buds. On mature tomato plants, flowers develop. This is where sexual reproduction occurs.

 

Tomato life cycle
Diagram of the tomato life cycle (©2020 Let’s Talk Science). 

 

Graphic - Text Version

The life cycle starts from seeds. As the plant grows and matures, flowers develop. After pollination and fertilization, fruits develop. These contain seeds, allowing for the life cycle to start again.

Flower Structure

Flowers are important for reproduction and the production of seeds. A tomato flower is sometimes called a perfect flower because both male and female organs are located inside it.

Tomato flower and fruit
Diagram of a tomato flower and its fruit (© 2020 Let’s Talk Science).

 

Graphic - Text Version

The ovary inside the flower develops into the tomato fruit that we eat. The petals, stamens, and stigma dry up and fall off as the fruit matures


The tomato flower has four main parts:

  1. Sepal:This part protects the bud before it opens. It is green and it is first visible when the bud forms. 
  2. Petal: This is the part of the flower that attracts insect pollinators. In tomato flowers, the petals are usually yellow.
  3. Stamen: This is the male part of the flower. It usually has a filament with an anther at the top. The anther is covered with pollen. Pollen contains the male genetic information. In tomato flowers, the stamens are fused together into a yellow, tube-shaped structure. 
  4. Pistil: This is the female part of the flower. It consists of the stigma, style, and ovary. It is located at the centre of the flower, inside the tube of stamens.

The female reproductive organ is the ovary. It is located at the base of the pistil. The ovary contains ovules. Once the ovules are fertilized, an embryo can develop and form the seeds that will be found inside the tomato fruit.

Fruit Development

For flowers to develop into the tomato fruit that we eat, two things need to happen: pollination and fertilization.

  1. Pollination: This is a process where pollen, from the anthers, is placed onto the stigma. This can be done by the wind, called wind pollination, or by insect pollinators through buzz pollination.
    Buzz pollination occurs when an insect pollinator, like a bee, lands on a flower and vibrates its flight muscles. This can shake pollen loose from the anther. Some of these pollen grains may land in other flowers, resulting in pollination.
  2. Fertilization: This process is when male reproductive cells from the pollen and female reproductive cells from the ovule combine. This is like when sperm and egg cells combine in animals. In plants, these cells are called gametes Two gametes come together in the ovary and develop into a seed. The seed contains the embryo, endosperm, and seed coat Once the seeds are formed, the tomato life cycle can begin all over again.

Did you know?

Not all insects can buzz-pollinate. For example, bumblebees can pollinate tomato flowers, but honeybees can't. Honeybees also don't visit tomato flowers because they have no nectar to feed on.

Bumblebee pollinating tomato flower
Bumblebee pollinating a tomato flower (Source: SimplyCreativePhotography via iStockphoto).

 

Fruit or Vegetable?

Is tomato a fruit or a vegetable? In cooking, tomato is considered a vegetable mostly because it is not sweet and not usually used in desserts. But in botany, tomato is a fruit. Fruit is defined as a part of a plant that develops from a flower’s ovary and has seeds. Since a tomato develops from its flower’s ovary and it has seeds inside, it is a fruit.

Glossary

Angiosperm: Flowering plant.

Anther: The part of the stamen where pollen is produced.

Buzz Pollination: A process where some insects land on flowers and shake pollen off of stamens by contracting their flight muscles causing vibrations.

Cotyledon: The part of an embryonic plant that will become the first leaves. These are also known as seed leaves.

Embryo: The tiny, immature plant inside a seed.

Endosperm: The part of a seed that stores food to be used by the embryo during germination.

Fertilization: The process when two gametes come together and develop into a seed.

Gametes: Cells that can fuse together during sexual reproduction. Each cell contains half the genetic information for the new plant. In flowering plants, the male gamete is in the pollen and the female gamete is in the ovule.

Germination: The process of a plant starting to grow from a seed. This usually happens after a period of dormancy. Good environmental conditions are important to start germination.

Filament: The part of the stamen that supports the anther.

Ovary: The part of the pistil that contains the ovules.

Ovule: A structure located within the female ovary. It contains female genetic information and can develop into a seed after fertilization.

Pedicel: The stem that attaches a flower to the main plant.

Petal: This is the part of the flower that attracts insect pollinators. In tomato flowers, the petals usually are yellow in colour.

Pistil: The female part of the flower. It is made up of the stigma, style, ovary and the ovules, which contain the female genetic information.

Pollen: Pollen contains the male genetic information. It is found on the anther at the top of the filament, which is part of the stamen.

Radicle: The part of an embryo that will become the root.

Seed Coat: The protective covering of a seed.

Seedling: The young plant that develops from a seed.

Sepal: This green part of the flower protects the bud before it opens. 

Sexual Reproduction: In plants, this sort of reproduction happens when male pollen is deposited on female plant organs to produce seeds.

Stamen: This is the male part of the flower. It is made up of the filament and the anther, which is covered in pollen. 

Stigma: This is where the pollen is deposited to allow fertilization. It is part of the pistil, the female reproductive organ, and is at the top of the style, above the ovary. 

Style: The part of the pistil above the ovary and below the stigma.

Wind Pollination: A process where flowers are pollinated with the help of wind.

Learn More

Is tomato a fruit or vegetable? (2018)

A video (3:03 min.) from DreamWorks TV exploring the controversy. It even went before the US Supreme Court! 

A bumblebee buzz-pollinates a tomato flower (2016)

Video footage (0:23 min.) from PLOS Media of a bumblebee buzz-pollinating tomato flowers. 

Tomato plants from tomato slice (2018)

Time-lapse video (1:37 min.) of tomato seeds germinating from inside tomato slices and growing into a mature plant in under two minutes!

Flowering Principles (2003)

Lesson from Don Lee & Kim Todd on the life cycle of flowering plants, complete with graphics and quizzes.

References

Bumblebee Conservation Trust. (n.d.). Why are bumblebees such good pollinators?

Lee, D. & Todd, K. (n.d.). Flowering Principles. University of Nebraska-Lincoln.

Oxford Dictionaries. (n.d.). Is a tomato a fruit or a vegetable? Lexico.

Root, T. (1996). Virtual Crops®. Lycopersicon esculentum (Tomato): An anatomy atlas. University of California Davis.

Science Learning Hub. (n.d.). Flowering plant life cycles.

Tilley, N. (2019). Steps to pollinate tomatoes by hand. Gardening Know How.